CMOS image sensors are devices which converts an optical image to an electrical signal and may be made using a CMOS manufacturing technique. In some CMOS image sensors, MOS transistors may be formed to be associated with a number of pixels. CMOS image sensors may include a switching system for sequentially detecting an output using the MOS transistors to convert signal charges generated in response to light to a voltage which may reproduce image information through signal processing.
CMOS image sensors may have several advantages. Compared to a driving system of a CCD image sensor, CMOS image sensor may implement various scanning systems to integrate a signal processing circuit in a single chip, thereby minimizing the size of a CMOS image sensors. If a compatible CMOS technique is used, manufacturing costs may be minimized and low power consumption may be accomplished.
With the development of techniques for manufacturing an image sensor, the size of photodiodes has gradually reduced with these developments, resulting in an increase in the number of pixels while maintaining the chip size. Accordingly, the area of the light-receiving portion may be reduced, which may cause a degradation in image quality in some circumstances. An image sensor may have a front illumination structure in which a photodiode is formed in a bottom portion of a substrate and/or a logic circuit formed in the top portion of the substrate, with light irradiated onto the top surface of the substrate during operation. However, since light loss may be caused by various overlying layers formed on the photodiode, satisfactory light responsiveness of the photodiode may not be consistently obtainable. Furthermore, since the penetration depth of a photon is large, there is a difficulty in changing a light flux to be emitted to a photocharge.
A back-side illumination (BSI) image sensor is a type of image sensor in which light may be received from the back side of a wafer. In a BSI image sensor a step on a light-receiving portion may be minimized, which may eliminate and/or minimize a light interference phenomenon due to metal routing. In a back-side illumination system, unlike a front illumination system, a photodiode may be formed in a first substrate on an upper side and a logic circuit may be formed on a second substrate positioned on a lower side, with the first substrate and the second substrate may be pressed and/or bonded to each other. A bonding technique for implementing BSI may include an oxide-to-oxide process, a metal-to-metal process, and/or a packaging technique for a through silicon via.
A packaging technique using a back-side illumination image sensor of the related art may have complications relating to a wiring process for an electrical connection with an upper connection terminal (e.g. a metal pad) after a through silicon via process.